CARBON 



V 



I 



Fig. 23. Combus- 

 tion. 



about an inch above the burner, then light the gas above the gauze 

 (Fig. 22). 



Questions. ( i ) Why was a charred circle formed when the piece 

 of paper was pressed down upon the flame ? (2) Why did the wire 



first redden near the outer 

 portions of the flame and not 

 at the center? (3) Why did 

 the flame refuse to burn 

 above the wire gauze, when 

 the gauze was pressed down upon the flame? 

 (4) When the gas was lighted above the gauze, 

 why did it refuse to burn below? (5) What is 

 kindling temperature ? (6) What are the three 

 conditions necessary for combustion? (7) What 

 condition was lacking when the gauze was 

 placed in the flame ? (8) Why does a flame give 

 light when the air is excluded from the burner, 

 and give but little light when the air vent is open ? (9) Does the 

 amount of light which a flame produces indicate the amount of heat 

 produced? Why? (10) What causes a flame to give light ? (n) 

 Why do some materials, when burned, produce more flame than 

 others? (12) What is spontaneous combustion? (13) Explain how 

 it is possible for clover or fodder to undergo spontaneous combus- 

 tion in a barn. (14) What can be done to prevent spontaneous 

 combustion? (15) Carbon, when burned, produces heat; limestone, 

 CaCO 3 , contains carbon ; why is it not possible to use limestone for 

 fuel? 



54. Spontaneous Combustion. In order for a sub- 

 stance to undergo combustion, it is not necessary for a 

 match or flame to be applied to the material. As soon as 

 a substance is heated to its kindling temperature, that is, 

 the temperature at which it unites with oxygen, if in the 

 presence of air, combustion takes place, called spontaneous 

 combustion. Clover, when stored in the mow in a damp 



